/*
 * mppe.c - interface MPPE to the PPP code.
 *
 * By Frank Cusack <fcusack@fcusack.com>.
 * Copyright (c) 2002,2003,2004 Google, Inc.
 * All rights reserved.
 *
 * License:
 * Permission to use, copy, modify, and distribute this software and its
 * documentation is hereby granted, provided that the above copyright
 * notice appears in all copies.  This software is provided without any
 * warranty, express or implied.
 *
 * Changelog:
 *      08/12/05 - Matt Domsch <Matt_Domsch@dell.com>
 *                 Only need extra skb padding on transmit, not receive.
 *      06/18/04 - Matt Domsch <Matt_Domsch@dell.com>, Oleg Makarenko
 * <mole@quadra.ru> Use Linux kernel 2.6 arc4 and sha1 routines rather than
 *                 providing our own.
 *      2/15/04 - TS: added #include <version.h> and testing for Kernel
 *                    version before using
 *                    MOD_DEC_USAGE_COUNT/MOD_INC_USAGE_COUNT which are
 *                    deprecated in 2.6
 */

#include "netif/ppp/ppp_opts.h"
#if PPP_SUPPORT &&                                                             \
    MPPE_SUPPORT /* don't build if not configured for use in lwipopts.h */

#include <string.h>

#include "lwip/err.h"

#include "netif/ppp/ccp.h"
#include "netif/ppp/mppe.h"
#include "netif/ppp/ppp_impl.h"
#include "netif/ppp/pppcrypt.h"
#include "netif/ppp/pppdebug.h"

#define SHA1_SIGNATURE_SIZE 20

/* ppp_mppe_state.bits definitions */
#define MPPE_BIT_A 0x80 /* Encryption table were (re)inititalized */
#define MPPE_BIT_B 0x40 /* MPPC only (not implemented) */
#define MPPE_BIT_C 0x20 /* MPPC only (not implemented) */
#define MPPE_BIT_D 0x10 /* This is an encrypted frame */

#define MPPE_BIT_FLUSHED MPPE_BIT_A
#define MPPE_BIT_ENCRYPTED MPPE_BIT_D

#define MPPE_BITS(p) ((p)[0] & 0xf0)
#define MPPE_CCOUNT(p) ((((p)[0] & 0x0f) << 8) + (p)[1])
#define MPPE_CCOUNT_SPACE 0x1000 /* The size of the ccount space */

#define MPPE_OVHD 2     /* MPPE overhead/packet */
#define SANITY_MAX 1600 /* Max bogon factor we will tolerate */

/*
 * Perform the MPPE rekey algorithm, from RFC 3078, sec. 7.3.
 * Well, not what's written there, but rather what they meant.
 */
static void mppe_rekey(ppp_mppe_state *state, int initial_key) {
  lwip_sha1_context sha1_ctx;
  u8_t sha1_digest[SHA1_SIGNATURE_SIZE];

  /*
   * Key Derivation, from RFC 3078, RFC 3079.
   * Equivalent to Get_Key() for MS-CHAP as described in RFC 3079.
   */
  lwip_sha1_init(&sha1_ctx);
  lwip_sha1_starts(&sha1_ctx);
  lwip_sha1_update(&sha1_ctx, state->master_key, state->keylen);
  lwip_sha1_update(&sha1_ctx, mppe_sha1_pad1, SHA1_PAD_SIZE);
  lwip_sha1_update(&sha1_ctx, state->session_key, state->keylen);
  lwip_sha1_update(&sha1_ctx, mppe_sha1_pad2, SHA1_PAD_SIZE);
  lwip_sha1_finish(&sha1_ctx, sha1_digest);
  lwip_sha1_free(&sha1_ctx);
  MEMCPY(state->session_key, sha1_digest, state->keylen);

  if (!initial_key) {
    lwip_arc4_init(&state->arc4);
    lwip_arc4_setup(&state->arc4, sha1_digest, state->keylen);
    lwip_arc4_crypt(&state->arc4, state->session_key, state->keylen);
    lwip_arc4_free(&state->arc4);
  }
  if (state->keylen == 8) {
    /* See RFC 3078 */
    state->session_key[0] = 0xd1;
    state->session_key[1] = 0x26;
    state->session_key[2] = 0x9e;
  }
  lwip_arc4_init(&state->arc4);
  lwip_arc4_setup(&state->arc4, state->session_key, state->keylen);
}

/*
 * Set key, used by MSCHAP before mppe_init() is actually called by CCP so we
 * don't have to keep multiple copies of keys.
 */
void mppe_set_key(ppp_pcb *pcb, ppp_mppe_state *state, u8_t *key) {
  LWIP_UNUSED_ARG(pcb);
  MEMCPY(state->master_key, key, MPPE_MAX_KEY_LEN);
}

/*
 * Initialize (de)compressor state.
 */
void mppe_init(ppp_pcb *pcb, ppp_mppe_state *state, u8_t options) {
#if PPP_DEBUG
  const u8_t *debugstr = (const u8_t *)"mppe_comp_init";
  if (&pcb->mppe_decomp == state) {
    debugstr = (const u8_t *)"mppe_decomp_init";
  }
#endif /* PPP_DEBUG */

  /* Save keys. */
  MEMCPY(state->session_key, state->master_key, sizeof(state->master_key));

  if (options & MPPE_OPT_128)
    state->keylen = 16;
  else if (options & MPPE_OPT_40)
    state->keylen = 8;
  else {
    PPPDEBUG(LOG_DEBUG,
             ("%s[%d]: unknown key length\n", debugstr, pcb->netif->num));
    lcp_close(pcb, "MPPE required but peer negotiation failed");
    return;
  }
  if (options & MPPE_OPT_STATEFUL)
    state->stateful = 1;

  /* Generate the initial session key. */
  mppe_rekey(state, 1);

#if PPP_DEBUG
  {
    int i;
    char mkey[sizeof(state->master_key) * 2 + 1];
    char skey[sizeof(state->session_key) * 2 + 1];

    PPPDEBUG(LOG_DEBUG, ("%s[%d]: initialized with %d-bit %s mode\n", debugstr,
                         pcb->netif->num, (state->keylen == 16) ? 128 : 40,
                         (state->stateful) ? "stateful" : "stateless"));

    for (i = 0; i < (int)sizeof(state->master_key); i++)
      sprintf(mkey + i * 2, "%02x", state->master_key[i]);
    for (i = 0; i < (int)sizeof(state->session_key); i++)
      sprintf(skey + i * 2, "%02x", state->session_key[i]);
    PPPDEBUG(LOG_DEBUG, ("%s[%d]: keys: master: %s initial session: %s\n",
                         debugstr, pcb->netif->num, mkey, skey));
  }
#endif /* PPP_DEBUG */

  /*
   * Initialize the coherency count.  The initial value is not specified
   * in RFC 3078, but we can make a reasonable assumption that it will
   * start at 0.  Setting it to the max here makes the comp/decomp code
   * do the right thing (determined through experiment).
   */
  state->ccount = MPPE_CCOUNT_SPACE - 1;

  /*
   * Note that even though we have initialized the key table, we don't
   * set the FLUSHED bit.  This is contrary to RFC 3078, sec. 3.1.
   */
  state->bits = MPPE_BIT_ENCRYPTED;
}

/*
 * We received a CCP Reset-Request (actually, we are sending a Reset-Ack),
 * tell the compressor to rekey.  Note that we MUST NOT rekey for
 * every CCP Reset-Request; we only rekey on the next xmit packet.
 * We might get multiple CCP Reset-Requests if our CCP Reset-Ack is lost.
 * So, rekeying for every CCP Reset-Request is broken as the peer will not
 * know how many times we've rekeyed.  (If we rekey and THEN get another
 * CCP Reset-Request, we must rekey again.)
 */
void mppe_comp_reset(ppp_pcb *pcb, ppp_mppe_state *state) {
  LWIP_UNUSED_ARG(pcb);
  state->bits |= MPPE_BIT_FLUSHED;
}

/*
 * Compress (encrypt) a packet.
 * It's strange to call this a compressor, since the output is always
 * MPPE_OVHD + 2 bytes larger than the input.
 */
err_t mppe_compress(ppp_pcb *pcb, ppp_mppe_state *state, struct pbuf **pb,
                    u16_t protocol) {
  struct pbuf *n, *np;
  u8_t *pl;
  err_t err;

  LWIP_UNUSED_ARG(pcb);

  /* TCP stack requires that we don't change the packet payload, therefore we
   * copy the whole packet before encryption.
   */
  np = pbuf_alloc(PBUF_RAW, MPPE_OVHD + sizeof(protocol) + (*pb)->tot_len,
                  PBUF_RAM);
  if (!np) {
    return ERR_MEM;
  }

  /* Hide MPPE header + protocol */
  pbuf_remove_header(np, MPPE_OVHD + sizeof(protocol));

  if ((err = pbuf_copy(np, *pb)) != ERR_OK) {
    pbuf_free(np);
    return err;
  }

  /* Reveal MPPE header + protocol */
  pbuf_add_header(np, MPPE_OVHD + sizeof(protocol));

  *pb = np;
  pl = (u8_t *)np->payload;

  state->ccount = (state->ccount + 1) % MPPE_CCOUNT_SPACE;
  PPPDEBUG(LOG_DEBUG,
           ("mppe_compress[%d]: ccount %d\n", pcb->netif->num, state->ccount));
  /* FIXME: use PUT* macros */
  pl[0] = state->ccount >> 8;
  pl[1] = state->ccount;

  if (!state->stateful ||                 /* stateless mode     */
      ((state->ccount & 0xff) == 0xff) || /* "flag" packet      */
      (state->bits & MPPE_BIT_FLUSHED)) { /* CCP Reset-Request  */
    /* We must rekey */
    if (state->stateful) {
      PPPDEBUG(LOG_DEBUG, ("mppe_compress[%d]: rekeying\n", pcb->netif->num));
    }
    mppe_rekey(state, 0);
    state->bits |= MPPE_BIT_FLUSHED;
  }
  pl[0] |= state->bits;
  state->bits &= ~MPPE_BIT_FLUSHED; /* reset for next xmit */
  pl += MPPE_OVHD;

  /* Add protocol */
  /* FIXME: add PFC support */
  pl[0] = protocol >> 8;
  pl[1] = protocol;

  /* Hide MPPE header */
  pbuf_remove_header(np, MPPE_OVHD);

  /* Encrypt packet */
  for (n = np; n != NULL; n = n->next) {
    lwip_arc4_crypt(&state->arc4, (u8_t *)n->payload, n->len);
    if (n->tot_len == n->len) {
      break;
    }
  }

  /* Reveal MPPE header */
  pbuf_add_header(np, MPPE_OVHD);

  return ERR_OK;
}

/*
 * We received a CCP Reset-Ack.  Just ignore it.
 */
void mppe_decomp_reset(ppp_pcb *pcb, ppp_mppe_state *state) {
  LWIP_UNUSED_ARG(pcb);
  LWIP_UNUSED_ARG(state);
  return;
}

/*
 * Decompress (decrypt) an MPPE packet.
 */
err_t mppe_decompress(ppp_pcb *pcb, ppp_mppe_state *state, struct pbuf **pb) {
  struct pbuf *n0 = *pb, *n;
  u8_t *pl;
  u16_t ccount;
  u8_t flushed;

  /* MPPE Header */
  if (n0->len < MPPE_OVHD) {
    PPPDEBUG(LOG_DEBUG, ("mppe_decompress[%d]: short pkt (%d)\n",
                         pcb->netif->num, n0->len));
    state->sanity_errors += 100;
    goto sanity_error;
  }

  pl = (u8_t *)n0->payload;
  flushed = MPPE_BITS(pl) & MPPE_BIT_FLUSHED;
  ccount = MPPE_CCOUNT(pl);
  PPPDEBUG(LOG_DEBUG,
           ("mppe_decompress[%d]: ccount %d\n", pcb->netif->num, ccount));

  /* sanity checks -- terminate with extreme prejudice */
  if (!(MPPE_BITS(pl) & MPPE_BIT_ENCRYPTED)) {
    PPPDEBUG(LOG_DEBUG, ("mppe_decompress[%d]: ENCRYPTED bit not set!\n",
                         pcb->netif->num));
    state->sanity_errors += 100;
    goto sanity_error;
  }
  if (!state->stateful && !flushed) {
    PPPDEBUG(LOG_DEBUG, ("mppe_decompress[%d]: FLUSHED bit not set in "
                         "stateless mode!\n",
                         pcb->netif->num));
    state->sanity_errors += 100;
    goto sanity_error;
  }
  if (state->stateful && ((ccount & 0xff) == 0xff) && !flushed) {
    PPPDEBUG(LOG_DEBUG, ("mppe_decompress[%d]: FLUSHED bit not set on "
                         "flag packet!\n",
                         pcb->netif->num));
    state->sanity_errors += 100;
    goto sanity_error;
  }

  /*
   * Check the coherency count.
   */

  if (!state->stateful) {
    /* Discard late packet */
    if ((ccount - state->ccount) % MPPE_CCOUNT_SPACE > MPPE_CCOUNT_SPACE / 2) {
      state->sanity_errors++;
      goto sanity_error;
    }

    /* RFC 3078, sec 8.1.  Rekey for every packet. */
    while (state->ccount != ccount) {
      mppe_rekey(state, 0);
      state->ccount = (state->ccount + 1) % MPPE_CCOUNT_SPACE;
    }
  } else {
    /* RFC 3078, sec 8.2. */
    if (!state->discard) {
      /* normal state */
      state->ccount = (state->ccount + 1) % MPPE_CCOUNT_SPACE;
      if (ccount != state->ccount) {
        /*
         * (ccount > state->ccount)
         * Packet loss detected, enter the discard state.
         * Signal the peer to rekey (by sending a CCP Reset-Request).
         */
        state->discard = 1;
        ccp_resetrequest(pcb);
        return ERR_BUF;
      }
    } else {
      /* discard state */
      if (!flushed) {
        /* ccp.c will be silent (no additional CCP Reset-Requests). */
        return ERR_BUF;
      } else {
        /* Rekey for every missed "flag" packet. */
        while ((ccount & ~0xff) != (state->ccount & ~0xff)) {
          mppe_rekey(state, 0);
          state->ccount = (state->ccount + 256) % MPPE_CCOUNT_SPACE;
        }

        /* reset */
        state->discard = 0;
        state->ccount = ccount;
        /*
         * Another problem with RFC 3078 here.  It implies that the
         * peer need not send a Reset-Ack packet.  But RFC 1962
         * requires it.  Hopefully, M$ does send a Reset-Ack; even
         * though it isn't required for MPPE synchronization, it is
         * required to reset CCP state.
         */
      }
    }
    if (flushed)
      mppe_rekey(state, 0);
  }

  /* Hide MPPE header */
  pbuf_remove_header(n0, MPPE_OVHD);

  /* Decrypt the packet. */
  for (n = n0; n != NULL; n = n->next) {
    lwip_arc4_crypt(&state->arc4, (u8_t *)n->payload, n->len);
    if (n->tot_len == n->len) {
      break;
    }
  }

  /* good packet credit */
  state->sanity_errors >>= 1;

  return ERR_OK;

sanity_error:
  if (state->sanity_errors >= SANITY_MAX) {
    /*
     * Take LCP down if the peer is sending too many bogons.
     * We don't want to do this for a single or just a few
     * instances since it could just be due to packet corruption.
     */
    lcp_close(pcb, "Too many MPPE errors");
  }
  return ERR_BUF;
}

#endif /* PPP_SUPPORT && MPPE_SUPPORT */
